Generally, containers to be used for importation/exportation goods may be classified into 20 feet-type and 40 feet-type. In the case of 20 feet-type, live load including the weight of container is not greater than 24 ton. In the case of 40 feet-type, live load including the weight of container is not greater than 30 ton. This fact is limited to the application of International Standard with respect to importation/exportation goods. Alternatively, containers to be used for importation/exportation goods may be classified into a dry-type container for transporting general goods, a ceiling open-type container for conveniently loading or unloading goods, and a freeze-type container for transporting frozen goods or cold-storage goods.
The freeze-type container generally employs a refrigerating unit for setting a desired cooling temperature with respect to loading goods. Accordingly this freeze-type container may be further classified into an internal-type container and an external-type container in accordance with installation of the refrigerating unit. Internal temperature of cargo room may be controlled in the range of +26° C.˜−28° C. due to the operation of refrigerating unit.
Meanwhile, it is required to have an electric power source for operating the refrigerating unit. For this purpose, an electric apparatus for applying and storing an electric source generated from a power source of a trailer or a container ship is also installed in the freezer container together with the refrigerating unit. Since it is necessary to have some special devices in the freezer container, the freezer container is loaded in a freezer container space defined within the container ship.
The consumption of live fish has lately grown due to the increase of the consumers' desire according to the development in food service industry and a larger increase in national income. The output of live fish farmed and caught from the coastal waters is beyond the amount of consumption of home consumers preferring live fresh seafood. Since logistics costs for transporting live fish from a live fish producing district to the consumer is too high, purchase price of live fish is highly increased.
In the case of transporting live fish from the live fish producing district to the consumer under the room temperature condition, the percentage rate of live fish to seawater to be charged into a live fish container is 15%:85%. Since the number of live fish is high and it is hard to survive live fish by 24 hours in the course of transporting, the live fish may be transported for a relatively short distance. For transporting live fish over exceedingly long distances and from one country to another, logistics costs for transporting live fish is too high.
In view of the foregoing, a variety of endeavors for developing a live fish transporting container having advantages of the freezer container above have been proposed. It is important, therefore, that an improved live fish container can provide safe transportation of the young of fishes or aquarium fishes over long distances for a long time and can perform a large-scale transportation of live fish with a low logistic cost. This leads to the economical importation of live fish from a country with less consumption of live fish and leads to the prosperous exportation of the competitive domestic live fish.
For example, an improved container as described above generally comprises a live fish water tank installed in a cargo room having a door, a wet-type filtering tank, an oxygen-supply means, a circulation pump of the water and a controller, etc. A cooling device is installed at a rear side of the cargo room. This cooling device may be formed by remodeling a cooling unit of a conventional driving part in the freezer container to be suited to cool live fish. The water can be circulated from the live fish water tank to the wet-type filtering tank due to the operation of the circulation pump. At this time, the temperature of the water stored in the live fish water tank can be lowered at 5° C. by operating the cooling device, this leads to minimize the metabolic rate and the oxygen consumption rate of live fish. And incidentally, it is possible to transport live fish over short distances for a short time in a state that the water has a relatively low weight equivalent to four times with respect to the weight of live fish.
Meanwhile, the wet-type filtering tank installed in the live fish container generally includes filter media such as sand, gravel, non-woven fabric or sponge and so on by laminating them on a bottom of the live fish tank; and a filtering tank including filter media as such, which is installed at the outside of the live fish tank. The water may be filtered and purified by bacteria cultured in the filter media by making it flow through the filter media.
See for example, Korean Patent publication No. 10-2003-0019278 laid-open to the public on Mar. 6, 2003, which disclose a container for importing/exporting live fish having filtering apparatus. According to this patent application, functional filling materials such as red clay or elvan (germanium) are applied to the filter media so as to enhance the sterilizing power and the cleansing power. In addition, filling materials such as activated carbon (charcoal) is added to the filter media so as to improve the capability for purifying the live fish water.
If the wet-type filtering tank is independently used in the live fish container, the filter media must be deposited in the live fish water or additional large filtering tank must be installed. In this case, the total weight of the live fish filtering tank including the filter media is too great, thereby resulting in the excessive weight of the live fish container. In other words, the excessive weight over the limit weights of 24 ton in the 20 feet container or of 30 ton in the 40 feet container may be occurred, so that it is likely to break the rules with respect to the weight restrictions of live container.
In order to fulfill the rules with respect to the weight restrictions of live container, it is necessary to reduce the total size of live fish container including the filter media. This leads to the reduction in the quantity of live fish to be transported by using the live fish container at once. Accordingly, it is hard to reduce the logistical cost with respect to the transportation of live fish.
In the use of the conventional wet-type filter media, the live fish water may be circulated due to the operation of the circulation pump in a state that the filter media is immersed in the live fish water. As a result, the filtering efficiency is relatively low so that it is necessary to increase the volume occupied by the filter media so as to obtain a sufficient filtering capability. This leads to a remarkable reduction in the space for storing live fish.
Meanwhile, a large number of live fishes are stored at high population density in the live fish water tank of the live fish container. Typically, a worker reduces the temperature of the live fish water so as to minimize the metabolism rate and the oxygen consuming rate. Since a variety of harmful ingredients resulted from live fish excrement, more particularly, ammoniac nitrogen components may be rapidly accumulated in the live fish at a high concentration, it is hard to effectively remove the harmful ingredients by only using the conventional wet-type filtering tank.
As well known that, the ammoniac nitrogen components may be presented as two types of chemical formula such as NH3—N, NH4+—N which are combined with NH3 or NH4+, respectively. The ammoniac nitrogen components produced by combining with the nonionic ammonia can pass through a cell-wall of fish and can damage the live fish under even low concentration such as 2 mg/L or 2 ppm. Furthermore, the ammoniac nitrogen components may oxidize to the nitrate nitrogen or the nitrite nitrogen and they exhaust the dissolved oxygen in the water.
According to the rules of the U.S. Environmental Protection Agency, the content of the harmful ingredients such as ammoniac nitrogen must be removed below 0.002 mg/L so as to store the live fish with safe and fresh condition. However, it is impossible to remove these harmful ingredients by only using the wet-type filtering tank having a relatively poor filtering capability. If a transportation time of live fish by using a live fish container becomes long, the live fish is likely to be getting a certain disease due to the harmful ingredients accumulated in the live fish, thereby resulting in the death of live fish.
Consequently, the time limit for transporting live fish by using the conventional live fish container is only two days at maximum. Accordingly, the conventional live fish container is unsuitable for transportation live fish over a long distance for a long time and therefore it is only used for transportation over a short distance for a short time. As a result, a large number of live fish must be transported not on the sea and the land but on the air. This has resulted in high cost of transporting live fish and thereby it has poor productivity.